1. Field of the Invention
The present invention relates to a flat-type fluorescent display tube used in an electronic desk calculator, electronic clock or the like and a method of manufacture thereof.
2. Description of the Prior Art
The fluorescent display tube usually employs fluorescent material which emits light when electrons emitted from the cathode collide therewith, can obtain a very clear green display and therefore is often used in an electronic desk calculator, clock or other various electronic appliances. Such display tubes of various shapes have been commercially marketed.
Recently, in compliance with commercial demand for such a display tube which is smaller in size and capable of indicating multiple digits, thin flat-type display tubes have been developed and widely used. One of the display tube in the conventional type comprises an substrate made of an insulating material such as glass on which anode display portions formed of segment anode groupes with fluorescent material layers are disposed to form an anode substrate, an electrode assembly framework including mesh-shaped control electrodes and filamentous cathodes opposite to the anode display portions on the anode substrate, and a flat box-shaped upper cover having at least a transparent window portion. The anode substrate, electrode assembly framework, and upper cover are laminated one after another, and the peripheral portions of the anode substrate and the upper cover are air-tightly sealed with a sealing medium having a low melting point, such as frit glass to form a highly evacuated casing which makes use of the substrate as a part of the flat casing. In the flat-type fluorescent display tube as explained hereinabove, lead-in wires connected to each electrode are air-tightly led out from the casing through the peripheral sealing portions between the substrate and the upper cover, and the electrical connection between lead-in wires for each of the anodes and the respective anodes has been established in a separate step from the sealing of the casing using a method which melts and burns conductive frit glass to mechanically fix and electrically connect wiring conductors linearly printed on the substrate and connected to the segment anodes to the respective terminating ends of the lead-in wires for the anode which extend inside of the tube. However, in order to adopt the above melting and burning process using the conductive frit glass, a precaution must be taken so as not to deteriorate or adversely influence upon the characteristics of the fluorescent material layers and the cathodes, and sometimes the substrate and various electrodes mounted thereon are damaged or deteriorated by heating and burning, thereby making it difficult to produce sufficiently good and uniform products.
There is recently proposed and put into practical use the other type of fluorescent display tube which eliminates the above-mentioned disadvantages of the prior art. This fluorescent display tube comprises a casing formed of an anode substrate and an upper cover which are sealed at the peripheral portions thereof, a plurality of anode display portions each composed of segment anodes having fluorescent material layers thereon, control electrodes and filamentous cathodes disposed above the anode display portions so as to face the anode display portions, and a plurality of lead-in wires each electrically connected to the respective segment anodes, the control electrodes and the cathodes and air-tightly led out from the casing through the sealing portions between the anode substrate and the upper cover. In this conventional fluorescent display tube, there is provided a plurality of conductive sections on the anode substrate which are connected to the respective segment anodes through conductive wiring film. The lead-in wires for the segment anode extending to the inside of the casing through the seal portion include a contact having a spring portion at each end thereof so as to correspond to the respective conductive sections. The contact is pressed against the conductive section by the action of the spring portion thereby establishing an electrical connection without the use of the conductive frit glass. In the prior art device, the electrical connection between the lead-in wires and the respective segment anodes is made by the press contact using a spring force within a highly evacuated envelope. Therefore, the tube is simple in construction, can be used for a long time without deterioration. In addition, the intermediate heating and burning process at a high temperature which deteriorates the fluorescent material and the cathodes can be eliminated.
The fluorescent display tube of the prior art explained hereinabove can be satisfactorily operated under a certain condition. However, due to the recent expansion of the use of the fluorescent display tube, the fluorescent display tube has now been used in various electronic indicating appliances which are equipped with the inside of a car or the like. In the fluorescent display tube used in the appliances which always undergo strong vibration or shock, it is required to take special precaution for protecting the display tube against the mechanical vibration and shock. Otherwise, the tube would be damaged due to a failure in the electrical connection of contacts within the tube. This is particularly true in the fluorescent display tube in which the electrical connection between lead-in wires for the segment anode and conductive section is made by a pressure contact by the action of the spring.